1. Field of the Invention
This invention relates to a rhodium-containing catalyst especially suited as a hydroformylating catalyst used when a corresponding aldehyde is produced by subjecting an ethylenically unsaturated compound, carbon monoxide and hydrogen to the reaction of hydroformylation. This invention also relates to a process for reversibly ionizing or nonionizing such a catalyst, which makes it possible to recycle the catalyst, and a hydroformylation process that utilizes such reversible ionization or nonionization.
The present invention is also concerned with a process for producing an aldehyde by the use of the rhodium-containing catalyst, and a process for recovering the hydroformylating catalyst from a hydroformylation reaction mixture.
2. Related Art of the Invention
The reaction of converting an ethylenically unsaturated compound into an aldehyde by allowing it to react with carbon monoxide and hydrogen in the presence of a catalyst is called hydroformylation or oxo synthesis. It is industrially very highly valuable to utilize this reaction for the production of aldehydes.
Catalysts used in such hydroformylation commonly include cobalt compounds and rhodium compounds. In view of their catalytic activities and their properties of selective formation of aldehydes, the latter rhodium compounds are known to be superior to the former cobalt compounds.
Such rhodium compounds can be exemplified by rhodium salts such as rhodium oxide and rhodium complexes such as rhodium carbonyl. These may be used alone. In order to improve stability of these compounds or improve their catalytic activities, however, they are rather used in the form of complexes modified with ligands such as organic phosphorus compounds, organic arsenic compounds or organic antimony compounds.
Among these ligands, organic phosphorus compounds are preferably used in view of their toxicity and production cost. Of the organic phosphorus compounds, the state in which a phosphorus atom is bonded or the types of substituents bonded to the phosphorus atom are selected properly according to the types of the starting material ethylenically unsaturated compounds and those of desired aldehydes. More specifically, compounds such as tertiary phosphines or phosphites, the number of phosphorus atoms that indicates whether the ligands are unidentate, bidentate or higher and the type of substituents that indicates whether the ligands are alkyl-substituted or phenyl-substituted are used properly in appropriate geometry.
As examples in which organic phosphorus compounds are used as the ligands of hydroformylating catalysts comprised of a rhodium compound, the following are proposed.
(A) When straight-chain aldehydes are selectively produced, a rhodium compound is modified with a tertiary phosphine (Japanese Patent Publication No. 45-10730); PA0 (B) when branched-chain or straight-chain aldehydes are selectively produced from olefins having a functional group, such as methyl methacrylate or allyl alcohol, a rhodium compound is modified with a bidendate tertiary phosphine (Bull. Chem. Soc. Jpn., 50, 2351, 1977; Japanese Patent Application Laid-open No. 54-106405); and PA0 (C) in order to increase the reaction rate when aldehydes are produced from branched olefins having a great static hindrance, such as 3-methyl-3-buten-1-ol, a rhodium compound is modified with a triphenyl phosphite substituted with an alkyl group at the 2-position of a phenyl group thereof (Japanese Patent Application Laid-open No. 62-201881). PA0 (a) a rhodium compound; and PA0 (b) an organic phosphorus compound having at least one tertiary amine residual group and at least one tertiary phosphorus residual group, having the ability of coordination to said rhodium compound. PA0 (a) a rhodium compound; PA0 (b) an organic phosphorus compound having at least one tertiary amine residual group and at least one tertiary phosphorus residual group, having the ability of coordination to said rhodium compound; and PA0 (c) an acidic compound with which at least part of the tertiary amine residual group of the organic phosphorus compound is converted into ammonium ions.
Incidentally, rhodium compounds are very expensive and hence, when they are used as hydroformylating catalysts in an industrial scale, it becomes necessary to recover them so that they can be recycled. For this purpose, as methods for recovering usual hydroformylating catalysts, including the hydroformylating catalysts proposed in the prior art as stated in the above (A) to (C), it has been common to recover hydroformylating catalysts by heating a reaction mixture formed after hydroformylation, separating reaction products and unreacted reaction materials from the reaction mixture by distillation and then collecting the hydroformylating catalysts as distillation residues.
When, however, hydroformylating catalysts are recovered in this way, there has been the problem that the catalysts may deteriorate to have a short lifetime because of the heating carried out when the reaction products are distilled from the reaction mixtures. In particular, in instances in which the reaction products have a high boiling point, the lifetime of the catalysts becomes very short. Moreover, because of such heating, the reaction product may undergo decomposition or condensation to form catalyst poisons, or compounds with a high boiling point may accumulate, bringing about the problem that it becomes impossible to recycle the catalysts.
To solve such problems, it is proposed, when aliphatic olefins having 2 to 12 carbon atoms are hydroformylated, to use a rhodium catalyst with a ligand comprising a sulfonated or carboxylated water-soluble triarylphosphine to carry out hydroformylation in an aqueous phase, followed by separation of the product from the catalyst by decantation (Japanese Patent Application Laid-open No. 60-228439). It is also proposed to use a water-soluble binuclear complex as a hydroformylating catalyst (Japanese Patent Application Laid-open No. 61-97295).
It is still also proposed to carry out hydroformylation in the presence of a non-aqueous polar solvent, using an ionic metal complex catalyst with a ligand comprising a water-soluble organic phosphorus compound having a trisulfonated salt residual group, followed by extraction of the product from the reaction mixture by the use of a hydrocarbon solvent to recover the catalyst in the form of a solution of the non-aqueous polar solvent (Japanese Patent Application Laid-open No. 62-145038).
It is further proposed to carry out hydroformylation in the presence of a non-aqueous polar solvent, using an ionic metal complex catalyst with a ligand comprising a water-soluble organic phosphorus compound having a monosulfonated salt residual group, followed by extraction of the product from the reaction mixture by the use of water as an extracting reagent to recover the catalyst from the reaction mixture in the form of an aqueous solution (EP0350,922).
However, the methods disclosed in the foregoing Japanese Patent Applications Laid-open No. 60-228439 and No. 61-97295 have the problem that the starting material olefin has so low a solubility in the aqueous phase that no hydroformylation can be carried out at a reaction rate that can be satisfactory from an industrial aspect.
The method disclosed in Japanese Patent Application Laid-open No. 62-145038 is involved in the problem that the phosphorus compound as a ligand, having a trisulfonated salt residual group, is so hard to dissolve in usual hydrocarbon olefins that the non-aqueous polar solvent must be used in a large quantity. In addition, even when the non-aqueous polar solvent is used in a large quantity, the organic phosphorus compound can have no satisfactory solubility in such a solvent, and hence the molar ratio of phosphorus to rhodium can not be made higher, to cause the problem of a difficulty in selective production of straight-chain aldehydes.
In the method disclosed in EP0350,922, the organic phosphorus compound as a ligand, having a monosulfonated salt residual group, is so hard to dissolve in usual olefins that the non-aqueous polar solvent must be used. In addition, the organic phosphorus compound has no satisfactory solubility in such a non-aqueous polar solvent. Hence, there is the problem that, in order to make the molar ratio of phosphorus to rhodium higher, the non-aqueous polar solvent must be used in such a large quantity that may cause an apparent decrease in productivity.
Besides the problems discussed above, there is the problem that, in an attempt to hydroformylate unsaturated aliphatic hydrocarbons not miscible with non-aqueous polar solvents such as dimethyl sulfoxide as in the case of octenes, the organic phosphorus compounds as described above can not substantially dissolve in the starting material unsaturated aliphatic hydrocarbons, so that the hydroformylation does not proceed at a reaction rate that can be satisfactory from an industrial aspect. Hence, there is also the problem that the unsaturated aliphatic hydrocarbons to which the methods disclosed in the above publications can be applied are in a very limited scope.
As discussed above, in the prior art methods, the polar phosphorus ligands that are originally hard to dissolve in nonpolar materials and nonpolar reaction products are barely dissolved therein by the use of the polar solvents, necessarily bringing about a limit in the amount of each component used.
The hydroformylation in the prior art described above is also industrially limited to instances in which starting materials and reaction products contain no inorganic: salt residual group. Hence, there is the problem that the hydroformylation can not be applied to instances in which corresponding aldehydes are produced from ethylenically unsaturated compounds having an inorganic salt residual group, because of a great difficulty in the recycling of catalysts. This is because almost all of the ethylenically unsaturated compounds having an inorganic salt residual group and their hydroformylation products (i.e., aldehydes) are solid and hence it is substantially impossible to separate these and catalysts by distillation. As additional reasons stated below, it is also substantially impossible to separate them by extraction.
That is, the ethylenically unsaturated compounds having an inorganic salt residual group can only dissolve in polar solvents such as water and methanol, and hence phosphorus ligands or the like substituted with a polar group such as a sulfonate residual group can only be used as the ligands of hydroformylating catalysts used in the hydroformylation of such ethylenically unsaturated compounds. In such an instance, if polar solutions mainly composed of water or methanol are used so that such hydroformylating catalysts to the metal rhodium of which phosphorus ligands are coordinated can be recovered by extraction, both the catalysts and the reaction products are extracted since the hydroformylation products are water-soluble, and can not be separated.
Meanwhile, one may contemplate using nonpolar phosphorus ligands in order to make it possible to extract catalysts from reaction mixtures containing water-soluble hydroformylation products. However, such nonpolar phosphorus ligands have the problem that, in the solution mainly composed of water or methanol that serves as a reaction solution in such an instance, they can not be dissolved to an extent large enough to carry out the hydroformylation in an industrial scale.